Stillson wrenches (commonly known as “pipe wrenches”) or other such wrenches utilize a heel jaw secured to a handle and a movable hook jaw which also pivots to a limited extent about a point on the handle. Typically, the hook jaw can be selectively positioned relative to the heel jaw by rotating a threaded member on the wrench. The pivoting action of the hook jaw causes the hook jaw and heel jaw to further close as a rotational force is applied to the handle. Thus, gripping force and torque are simultaneously applied to a work piece.
Pipe wrenches typically used in the field utilize a threaded hook jaw that can be adjusted with a threaded member or nut to fit the size of the work piece. Nonetheless, the placement of the wrench on the work piece may be cumbersome due to the weight of the wrench or variations in the size of the work piece. Thus, it is common for an operator to rest the wrench on a shank portion of the hook jaw before force is applied to the handle. This practice still occurs even though it is known to be an improper use of a wrench as described in a publication, “Proper Use of Pipe Wrenches” by the Ridge Tool Company. FIG. 1 illustrates this common improper placement of a wrench on a work piece. Specifically, a conventional pipe wrench 10 comprises a handle 20 having a lower jaw member 30, a sleeve portion 40 affixed to or integrally formed with the handle 20, a rotatable threaded member 50, and a movable upper jaw 60. The upper jaw 60 includes a proximal end 62, an outer distal end 68, a shank portion 66 extending between the ends 62 and 68, and a threaded region 64. The upper jaw 60 also includes an upper jaw member 70. As will be appreciated, the distance between the lower jaw member 30 and the upper jaw member 70 can be selectively adjusted by rotating the member 50. The upper jaw 60 and specifically the shank portion 66 defines an interior face 67. Upon positioning a work piece 5 between the jaw members 30, 70, typically a user may rest the wrench 10 on the work piece 5, thereby resulting in contact between the shank face 67 and the work piece 5. This practice prevents the pivoting action of the hook jaw and limits the ability of the jaws to produce gripping force. As a result, the wrench may slip on the work piece when torque is applied. Additionally, the mechanical stress in the hook jaw is increased due to a transfer of force from the work piece to the shank of the hook. Failure of the hook jaw may result.
Accordingly, a need exists for a pipe wrench which is not susceptible to such problems with improper use and which provides an increased gripping force on a work piece positioned between its jaws upon application of torque to the wrench.